Knee arthroplasty has become one of the most commonly performed surgeries, with which a damaged or deformed knee joint due to congenital deformation, traumatic injuries, diseases, degenerative arthritis, etc. is removed and replaced with an artificial joint. In brief, referring to FIG. 1, the anterior cortex 15 is first cut according to the damaged or deformed state of a knee joint of a patient. And, an extension gap is determined to allow for bone cutting matching with the size of an artificial joint (prosthesis). The femur 10 is undercut according to the extension gap. In addition, according to the determined extension gap, referring to FIG. 2, a flexion gap is determined based on an upper end of the tibia 20. Then, referring to FIG. 3, the posterior condyles 11, the posterior chamfer 12, the anterior cortex 13 and the anterior chamfer 14 of the femur 10 are cut using an appropriate femoral cutting block 30. An artificial joint is then implanted to replace the cut knee joint.
The flexion gap, which is required for the knee to be flexed from an extended (straight) position, indicates the gap between the cut surface of the upper end of the tibia 20 and the cut surface of the posterior femoral condyles 11. Since the femur and the tibia rotate at a state of being in close contact with each other, the flexion gap is typically determined to be identical to the extension gap. However, the flexion gap may be determined according to 3-D shape of the damaged knee joint of a patient.
On the other hand, the femoral cutting block 30, used upon the posterior and anterior cuts at the posterior condyles 11, the posterior chamfer 12, the anterior cortex 13 and the anterior chamfer 14 of the femur 10, is commercially available in a standardized size corresponding to the size of the flexion gap. Therefore, the femoral cutting block 30 is determined to have a size corresponding to that of the determined flexion gap, while the size of the artificial joint is determined according to the size of the femoral cutting block.
However, conventional devices for determining the size of a cutting block are problematic in terms of being incapable of determining a cutting block with a proper size because the size of the cutting block is determined by measuring only the height of the femur without any consideration for the size of a flexion gap that varies depending on the size of the cutting block.
Referring to FIG. 4, the problem of the conventional devices for determining the size of the cutting block will be described in detail, as follows. A conventional device 40 for determining the size of the cutting block includes a support 41 to be placed at the posterior femoral condyles 11 and a bar 42 to be placed at the anterior femoral cortex 15. The bar 42 is slidably connected with the support 41 and has a predetermined number of graduations. The support 41 includes an indicating line. A graduation of the bar is determined, which is aligned with the indicating line of the support 42, by closely contacting the support 41 and the bar 42 with the position femoral condyles 11 and the anterior femoral cortex 15, respectively. The measured graduation becomes to the size of a cutting block 30, and thereby the size of an artificial joint is determined.
However, there is a significant problem experienced in this conventional device 40 for determining the size of the cutting block. That is, the graduation of the bar indicated by the indicating line is changed by the damaged or deformed state of the posterior femoral condyles, by the cut degree of the anterior femoral cortex or by the total height of the femur, thereby the size of the cutting block is varied.
As described above, the flexion gap is the gap between the cut surface of the upper end of the tibia 20 and the cut surface of the posterior femoral condyles 11, and the size of the cutting block should be determined by the flexion gap. However, since the conventional devices determine the size of the cutting block by only the height of the femur without any consideration of the flexion gap, the devices have the problem of being incapable of determining the cutting block with a proper size to allow a surgeon to perform a bone cutting operation to define a desired flexion gap.
If a cutting block with an unsuitable size is determined, a determined artificial joint has also an unsuitable size. This unsuitable prosthesis results in a limitation in normal physical behavior. Consequentially, extension and flexion exercises of the knee are not normal, and an imbalance occurs between the muscle and the ligament that constitute the knee joint.